Most of you used your high level knowledge to make it work, but here it is for begineers like me who would like to solve it with an easy method:

import java.io.; import java.util.;

public class Solution {

public static void main(String[] args) {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT. Your class should be named Solution. */
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int arrObj;

    // data list
    ArrayList<ArrayList<Integer>> dataList = new ArrayList<>();
    // making array list to store data
    for (int i = 0; i < n; i++){

        int nArray = sc.nextInt();
        ArrayList<Integer> arr = new ArrayList<>();
        for(int j = 0; j < nArray; j++){

            arrObj = sc.nextInt();

            arr.add(arrObj);

        }
        // System.out.println(arr);
        dataList.add(arr);
    }


    int n2 = sc.nextInt();
    //query list
    // ArrayList<ArrayList<Integer>> queryList = new ArrayList<>();
    // making data list to fetch data or else print Erorr
    for (int i = 0; i < n2; i++){

        int row = sc.nextInt();
        int coloumn = sc.nextInt();
        // System.out.println(arr2);
        try{
            System.out.println(dataList.get(row-1).get(coloumn-1));
        }
        catch(Exception e){
            System.out.println("ERROR!");
        }


    }


}

}

`

Solution:

public class Solution {

public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    ArrayList<ArrayList<Integer>> list = new ArrayList<>();
    for(int i=1;i<=n;i++){
        ArrayList<Integer> newList = new ArrayList<>();
        int d = sc.nextInt();
        for(int j=1;j<=d;j++){
            int l = sc.nextInt();
           newList.add(l);
        }
        list.add(newList);
    }
    int q = sc.nextInt();
    for(int i=0;i<q;i++){
        int x = sc.nextInt()-1;
        int y = sc.nextInt()-1;
    if(list.get(x).size()>y){
        System.out.println(list.get(x).get(y));
    } else {
        System.out.println("ERROR!");
    }


    }
}

}

Here is java Arraylist solution - https://programmingoneonone.com/hackerrank-java-arraylist-problem-solution.html

Scanner sc=new Scanner(System.in); int n=sc.nextInt(); ArrayList> list=new ArrayList>();

    for(int i=0;i<n;i++){
        int l1=sc.nextInt();
        ArrayList<Integer> arr=new ArrayList<Integer>();
        for(int j=0;j<l1;j++){
           arr.add(sc.nextInt());
     }
     list.add(arr);
    }
    int q=sc.nextInt();

     for(int i=0;i<q;i++){
        int a=sc.nextInt()-1;
        int b=sc.nextInt()-1;

        if(a<list.size() && a>=0){
        if(b<(list.get(a).size()) && b>=0){
            System.out.println(list.get(a).get(b));
        }
        else{
            System.out.println("ERROR!");
        }
    }

    }

import java.util.*; public class temporary { public static void main(String[] args) { Scanner myobj = new Scanner(System.in); ArrayList> list = new ArrayList<>(); int n = myobj.nextInt(); myobj.nextLine(); for (int i = 0; i < n; i++) { String line = myobj.nextLine(); String[] parts_list = line.split(" "); ArrayList sublist = new ArrayList<>(); for (int j=1;j< parts_list.length;j++){ sublist.add(Integer.valueOf(parts_list[j])); } list.add(sublist); } int q = myobj.nextInt(); myobj.nextLine(); for(int i=0;i

        }
    }

}

}